Torch assembly

ABSTRACT

The conventional gas turbine combustor is improved by mounting a pilot flame producing torch in a wall of the combustor to project a flame into the combustor as a means of ignition. The torch preferably is a catalytic igniter which will operate over a wide range of air/fuel ratios.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationsSer. No. 08/227,596 filed Apr. 14, 1994 (abandoned); Ser. No. 08/227,599filed Apr. 14, 1994; Ser. No. 197,931 filed Feb. 17, 1994 (U.S. Pat. No.5,593,299) and Ser. No. 835,556 filed Feb. 14, 1992 (U.S. Pat. No.5,453,003).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an assembly for ignition of gas turbinecombustors. In addition, this invention relates to devices forcontinuous stabilization/re-ignition of lean low NO_(x) combustion. Thisinvention also relates to igniters for use in place of conventionalspark plug fuel ignition systems.

2. Brief Description of Related Art

Commercial aircraft gas turbine combustors utilize combustor wallmounted igniters, typically a spark plug, for combustor light-off. Thisrequires the presence of fuel close to the wall. Inasmuch as combustionof fuel near the wall during full power operation tends to raise thewall temperature, combustor designs tend to be a compromise betweenignition and operational requirements. Thus there have been numerousattempts to achieve ignition away from the wall. Ideally, ignitionshould be achieved right at the fuel source so that ignition of theinitial fuel flow is possible. This avoids the necessity to dumpunburned fuel into the combustor prior to ignition (creating thepotential for hot starts or explosive detonations with consequent damageto the turbine) and enables the use of spray patterns which keep fuelaway from the combustor walls.

Accordingly, there has been interest in integrating the ignition sourceinto the fuel injector. For example, U.S. Pat. No. 4,938,019 describes afuel nozzle with an integrated spark plug igniter assembly and U.S. Pat.No. 4,825,658 describes a fuel nozzle with a catalytic glow plug igniterassembly. Such designs have major drawbacks which limit utility. Forexample, a spark plug integrated into an injector is subject to foulingif wetted by liquid turbine fuel, rendering it inoperative. In addition,size limitations reduce spark plug life. On the other hand, although theglow plug of U.S. Pat. No. 4,825,658 eliminates the fouling problem ofspark plugs, the glow plug is designed such that the return flow of therecirculating flow downstream of the injector contacts the hot glow plugsurface resulting in ignition of the downstream recirculating gases.Inasmuch as the initial direction of the incoming fuel-air flow from theswirler is away from the glow plug considerable fuel can traveldownstream before sufficient fuel is injected to increase therecirculation zone fuel concentration high enough at the glow plug toallow ignition. Thus explosive detonation is possible as is the casewith conventional spark igniters presently used in aircraft gas turbineengines. Advantageously, fuel should be ignited immediately as it entersthe combustor.

In the present invention atomized fuel entering a gas turbine combustoris reliably ignited as it enters the combustor by contact with acontinuous pilot flame projected into the combustor distal to thecombustor walls, at a location to ignite the incoming fuel. The presentinvention offers the advantages of away-from-the-wall ignition coupledwith continuous flame stabilization by providing for projection of thepilot flame into a combustor, whether from the liner wall or from thecombustor centerline.

SUMMARY OF THE INVENTION

The invention comprises a torch assembly for ignition of fuel inadmixture with air within a gas combustor, which comprises;

a tubular chamber containing a hot surface igniter, means for atomizingfuel into admixture with air, a combustion zone, and an exit opening forprojection of a resulting pilot flame into a combustor.

BRIEF DESCRIPTION OF THE DRAWING

The drawing shows a partial cross-sectional side-view of an embodimentcatalytic igniter/flame stabilizer torch assembly of the inventionhaving an axially mounted hot surface ignitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Those skilled in the art will gain an appreciation of the invention fromreading the following description of the preferred embodiments of theinvention in conjunction with a viewing of the accompanying drawing.With reference to the drawing, which is a cross-section in part of anembodiment assembly of the invention as seen from the side, there isseen a torch assembly 10 of the invention. The assembly 10 of theinvention comprises a tube 12 shown mounted in an aperture through theenclosure 14 and inner liner 16 of a gas turbine combustor. The tube 12defines a lumen or space 18 with an open end 20 providing entry into thecombustion chamber 22 of the combustor. Gas turbine combustors can beconstructed in a variety of configurations and with a variety ofmaterials. Representative of gas turbine combustors are those describedfor example in the U.S. Pat. No. 3,975,141 which is incorporated hereinby reference thereto. The opposite end 24 of tube 12 is shown on theexterior of the combustor and is closed by the plug 26. Passing throughplug 26 is an electrode 28 connected to an electrical power sourceexterior to the combustor (power source not shown in the drawing). Theelectrode 28 is electrically connected to a wire resistor heatingelement 30 and grounded to the casing of tube 12 which may beconstructed of metal such as stainless steel or the like. In thepreferred embodiment assemblies 10 of the invention, element 30 iseither an oxidation catalyst supporting resistance heater or anelectrically conductive metal oxidation catalyst component. For example,the element 30 can be a 0.045 mm Hast-X resistive wire coated with anyignition catalyst known in the art which is reactive with the fuel to beignited. For example, a support coated with an oxidation catalyst suchas a metal from the group VIII of the periodic table of elements and thelike. Most preferably, for long life and durability, the element 30 isitself a metal catalyst to provide, in operation, a hot ignitioncatalyst surface. Platinum group metal containing catalysts such as anoxide hardened platinum metal are preferred because of their highactivity with a wide variety of fuels and resistance to the effects ofsulfur in the fuel. Advantageously, the element 30 is made from aplatinum metal thus eliminating the need for a separate catalystcoating. The temperature of the element 30 is most readily monitored andcontrolled by measurement of element 30 resistance, but othertemperature sensing devices such as thermocouples, infrared detectorsand laser beam sensors may be used to monitor the temperature achievedwith the element 30. As shown in the drawing, the element 30 ispositioned axially within the tube 12 lumen or space 18 at a pointbetween the tube ends 20, 24 and spaced inwardly of open end 20. Theelement 30 need not, of course, be in any particular shape orconfiguration, so long as it presents a surface for contact with andignition of hydrocarbon fuels. The terms "fuel" and "hydrocarbon" asused in the present invention not only refer to organic compounds,including conventional liquid and gaseous fuels, but also to gas streamscontaining fuel values in the form of compounds such as carbon monoxide,organic compounds or partial oxidation products of carbon containingcompounds. Advantageously, the element 30 surfaces are catalyticigniters for oxidation of fuel and the surface remains at a temperaturehigh enough for continuous ignition of entering fuel without the needfor electrical power during operation, thus providing assurance againstcombustor flameout and enabling stabilization of very lean combustion,even beyond the normal lean limit of the combustor in which the assembly10 is installed. A non-catalytic igniter can be maintained at aneffective temperature for continuous ignition by heat from thecombustion zone. For combustor light-off, the element 30 may be heatedelectrically by passage of a current or by such means as inductiveheating. Although a smooth surface element 30 may be used, it has beenfound that elements 30 with flow through gas channels, as for exampleslots, are advantageous particularly at higher air flow velocitiesassociated with an air blast fuel injector, to be described more fullyhereinafter. The element 30 can therefore be in the configuration of aslotted bar, tube or like structure in addition to being a solid wire orribbon. Annularly disposed about the electrode 28 and proximal to plug26 is an atomizer 34 which may be an air blast type of nozzle orpressure atomizer, preferably an air swirler, for injecting fuel/airmixtures into contact with the element 30. Any of the known liquid fuelatomizers may be employed. Preferred as a means of atomizing liquidfuels and homogeneously mixing the atomized fuel with air in all ratiosare the devises known as swirlers.

Fuel enters the tube 12 through inlet conduit 36 and is carried toatomizer 34 through plug 26. In the atomizer 34 the fuel is atomized andcarried in an air mixture (the air being introduced into atomizer 34through port 40 fed by the turbine compressor; the compressor is notshown in the drawing) into downstream contact with the element 30. Theair admixed, atomized fuel is ignited by contact with the hot surface ofelement 30.

Combustion of ignited fuel is stabilized in combustion zone 44 by theswirl generated by air atomizer 34. Continuous ignition provided byelement 30 allows stable combustion even with lean fuel-air admixtures.Combusting gases are accelerated by the pressure of incoming air/fuelswirl, exiting combustion zone 44 by passage through nozzle 50, thusproviding a high velocity ignition torch. A restrictive nozzle 50 at end20 is not necessary, but preferred for increasing the velocity of theexiting flame. This enhances the projection of the flame into thecombustion chamber 22 away from the combustor walls. Torches of thepresent invention may be operated with either lean or rich fuel-airmixtures as dictated by requirements of the combustor in which it isused.

In operation of an assembly 10 of the present invention, fuel isatomized and mixed with air and passed into a combustion zone 44, aportion of the entering fuel contacting a hot ignition surface, thusproviding continuous ignition of entering fuel. Such continuous ignitionallows operation of the assembly 10 much closer to its lean limit thanwould otherwise be prudent because of the danger of a flameout. Withproper placement and sizing of a catalytic torch, operation below thenatural lean limit is possible. With electrical preheating of theelement 30 prior to initial introduction of fuel, light-off can occurwithout significant delay. Light-off can even be achieved at thecombustor lean limit.

The operation of the assembly 10 of the invention can be appreciated byreferring again to the drawing.

As shown in the drawing, atomizer 34 provides swirl to the air flowingthrough port 40 thus generating the shear forces necessary to atomizeand mix with fuel entering from conduit 36. The fuel is brought intocontact with the hot surface of element 30 by air flowing throughatomizer 34 resulting in ignition of fuel during passage into thecombustion zone 44. During starting of a gas turbine engine, typicallythe element 30 is heated to a temperature above the minimum temperaturerequired for ignition at the given air flow condition prior tointroduction of fuel thus assuring a rapid light-off. After light-off,electrical power to the element 30 may be controlled to maintain theelement 30 temperature below a safe value for the materials used.Typically, electrical heating is discontinued after light-off thoughcontinued controlled heating may be utilized to provide nearinstantaneous relight in those situations where aircraft operation, forexample, could result in engine flame-out such as by ingestion of waterinto the engine. Although this invention has been described in terms ofan air blast fuel injection, gas turbine fuel nozzles such as pressureatomizers or high shear nozzles can be utilized in the present inventionto atomize the fuel.

The resulting flame projected out of the end 20 of tube 12 and into thegas turbine combustor serves as the ignition means for igniting the fuelair mixtures separately injected into the gas turbine combustor. It is areliable, instant means of ignition.

Those skilled in the art will appreciate that many modification of thepreferred embodiment described above can be made without departing fromthe spirit and scope of the invention.

We claim:
 1. A torch assembly for ignition of fuel in admixture with airwithin a gas turbine combustor, which comprises;a tubular chamber; a hotsurface igniter which comprises an oxidation catalyst contained in thetubular chamber; means for atomizing fuel into admixture with air;conduit means for carrying the atomized fuel from the means foratomizing fuel, into the tubular chamber; electrical means for heatingthe igniter surface; a combustion zone in the tubular chamber betweenthe igniter and an exit opening; and an exit opening out of thecombustion zone for projection of a resulting pilot flame into acombustor.
 2. The assembly of claim 1 wherein said catalyst comprises aplatinum metal.
 3. The assembly of claim 2 wherein said ignitercomprises an oxide hardened platinum metal structure.
 4. The assembly ofclaim 1 wherein the means for atomizing comprises an air blast fuelnozzle.
 5. The assembly of claim 1 wherein the means for atomizingcomprises a pressure atomizer.
 6. The assembly of claim 1 wherein saidigniter is mounted coaxially in the tube.
 7. A torch assembly for theignition of air/fuel mixtures in the walled combustion chamber of a gasturbine, which comprises;a tube defining a tube lumen, positioned withinthe wall of the combustion chamber, said lumen having a first end and asecond end and a first opening into the combustion chamber from thefirst end, and a closed second end; means for atomizing fuel in amixture with air, mounted in the tube lumen, proximal to the second end;conduit means for delivery of a liquid fuel to the atomizer; passagemeans for carrying air to the atomizer; catalytic hot surface ignitionmeans for igniting atomized fuel/air mixtures, positioned in the lumenbetween the atomizer and the first opening; and electrical heating meansfor heating the hot surface.
 8. The assembly of claim 7 wherein themeans for atomizing fuel comprises a swirler.
 9. The assembly of claim 8wherein the catalytic igniter comprises a platinum metal.
 10. Theassembly of claim 7 which further comprises means for controlling thetemperature of the means for ignition.